EulerPhi[p] == Sum[DivisorProduct[1 - (1/Subscript[d, j]) Sum[Exp[(2 Pi I j k)/Subscript[d, j]], {k, 0, Subscript[d, j] - 1}], {Subscript[d, j], p}], {j, 1, p - 1}] /; Element[p, Primes] && Element[Subscript[d, j], Divisors[n]]

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2001-10-29